Aircraft fueling systems at commercial and military airports often incorporate miles of underground pipe through which fuel is pumped at high flow rates to individual aircraft fueling (parking) stations. The flow rates to each fueling station are often in the hundreds of gallons per minute.
Valve systems are provided at the individual fueling stations to reduce to a predetermined level the pressure of the flowing fuel, and to rapidly stop fuel flow when the aircraft fuel tank (of a particular airplane being fueled) becomes full and the high-level shut-off valve in such tank closes. Because of the large mass of the rapidly flowing fuel in the long lengths of pipe, it is important that the valve at an aircraft fueling station close before final closure of the shut-off valve in the aircraft tank being filled; otherwise, pressure surges could occur that would pressurize an aircraft fuel manifold to an unsafe level.
It is important that the valve means at each aircraft fueling station be simple, rugged, effective and substantially foolproof. It must accurately control the pressure of the fuel in the line between the fueling station and the aircraft fuel tank, and it must substantially instantaneously (less than a second) shut off just before the aircraft tank valve fully closes.
The valve means should have only one adjustment to set, in order to regulate pressure, because when more than one adjustment must be set the maintenance personnel can become confused and make mistakes. The valve means must be characterized by high stability, automatic rapid shut off, low friction (minimum use of sliding O-rings), and an ability to be used in different modes such as (for example) being part of an automatic excess-flow shut off that operates when a line breaks between the fueling station and an aircraft.
For many years, the assignee of the present patent application has supplied, for use in aircraft fueling stations at civilian and military airports, a pilot-operated pressure-reducing valve system that utilizes a "flowing control system" to control the main diaphragm valve at each fueling station. At all times when the system is operating, there is flow across the main valve through a circuit including an orifice restriction and a pressure-reducing pilot. Continuous flow of the fuel is required through this "flowing control system" in order to continuously modulate the pressure in the cover chamber of the main valve. The indicated "flowing control system" can present problems relative to cost, complexity, setting, requirement for substantial amounts of pipe, etc.
Pilot-operated diaphragm (and piston) valve systems have long been known which are not continuous flow but which are not satisfactory for airport fueling-station and many other purposes. Such valve systems are often characterized by complexity, large numbers of parts, inability to effect extremely rapid closing of the main valve, the presence of excessive numbers of sliding O-rings that increase friction and reduce stability, etc. There is a major need for a truly simple and fully effective pilot valve that has only a single setting means, and that is not (except in certain instances where additional functions are performed) part of a "flowing control system".